MRI exams for patients with pacemakers and implanted cardioverter defibrillators (ICDs) are contraindicated at all clinical field strengths. A a consequence, nearly 200,000 patients per year forego a clinically- indicated MRI exam due to safety concerns. Principal concerns include: (1) magnetic field interference with the device electronics, which may cause pacing problems or damage the device; and (2) radiofrequency (RF) induced lead-tip heating, which may transiently or irreversibly damage tissue at the lead-tip and inhibit pacing. Clinical evidence supports the fact that patients with pacemakers and ICDs can be scanned at 1.5T for a variety of clinical indications without serious adverse events when specific scanning protocols are followed; however, little is known about the risks associated with MRI scanning of patients with pacemakers and ICDs at 3T. The goal of the proposed work is to define the 3T MRI exam conditions for which a patient with a pacemaker or ICD may be safely completed (<3C lead-tip heating), and/or may be procured at a level of safety comparable to the same exam at 1.5T. 3T MRI exams are often preferred clinically due to the inherent improvement in SNR, which typically results in improved spatial resolution and conspicuity for anatomical detail. Despite these advantages, MRI exams for patients with pacemakers and ICDs are more strongly contraindicated at 3T than at 1.5T, largely because of prevailing concerns that device malfunction and lead-tip heating are most likely worse at 3T. To accomplish this goal we will, directly measure lead-tip heating at the pacemakers or ICDs lead-tip in cadavers using multiple fiber-optic temperature probes during MRI exams at 1.5T and 3T. The objective is to directly measure lead-tip heating under conditions that mimic, as closely as possible, the anatomic and tissue characteristics of clinical subjects. MRI thermometry will also be used to monitor heating distant from the lead tip. Experiments will include complete neuro (head), thoracic (spine and cardiac), abdominal, and knee MRI exams using standard clinical protocols and 15-minute intermediate SAR (2W/kg) and high SAR (4W/kg) scans per ASTM guidelines. Similar experiments will be performed in tissue equivalent gel phantoms that mimic the cadaveric pacemaker lead configuration using a 3D printed lead-path fixtures. The Public Health Significance is that the results of this work will define the 3T MRI exam conditions that are as safe or safer than a 1.5T exam using experimental conditions that closely mimic scanning human subjects with implanted pacemakers and ICDs. The impact will be to mitigate the risks faced by patients with pacemakers and ICDs undergoing either 3T or 1.5T MRI exams.